Adhesive comprising a mixture of a nucleated and nonnucleated phenolic resins



Patented Dec. 2, 1952 ADHESIVE COMPRISING A MIXTURE OF A NUCLEATED AND NONNUCLEATED PHE- NOLIC RESINS Paul G. Schrader and Alexander M. Partansky, Antioch, Calif., assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Application August 15, 1949, Serial No. 110,466.

18 Claims. 1

This invention relates to resins of the phenolaldehyde type which are useful in the manufacture of adhesives for plywood and for similar purposes. The present improvements are particularly concerned with new water-soluble phenolformaldehyde resins which, when mixed with resins of similar type known to the art, form a mixed resin having in the cured state an improved resistance to water. Such mixed resins can be used successfully as adhesives for gluing veneers of higher moisture content than is feasible in present commercial practice.

The use of phenolic adhesives is well established in the plywood industry. Numerous formulations for such adhesives have been disclosed in the prior art, such as those described in United States Patents Nos. 2,150,698, 2,360,376, 2,437,981 and 2,457,493. While such known adhesives are satisfactory for gluing dry veneers having a moisture content of less than about 3 to 4 per cent, they cannot be reliably employed with wet veneers having a moisture content as high as 6 to 10 per cent. With the latter, blisters develop on hot-pressing, or even complete failure to form a bond, under the usual conditions of temperature and pressing time which are employed in plywood manufacture.

In the manufacture of plywood the veneer panels are kiln-dried to a low moisture content, on the order of to 4 per cent, before the adhesive is applied to their surfaces. It is a problem in production line operation to hold the moisture content of th kiln-dried panels consistently within the desired limits, due to variations in the moisture of the undried veneers, or of atmospheric humidity, or other causes. When, as may happen at times, the veneers are discharged from the drier with too high a moisture content, mill operation may be badly dislocated and losses occur due to interrupted operation or to the production of defective plywood.

It is an object of this invention to provide an adhesive which can be employed successfully for gluing veneers having a wider range of moisture content than can be tolerated in present mill practice with the commercial adhesives now available. Such gain in adaptability to wet veneers should be secured without sacrifice of properties when the improved adhesive is employed with dry veneers. In other words, the object is to provide a satisfactory adhesive for use with both dry and wet veneers to produce plywood of quality equal to commercial specifications.

According to the invention our improved adhesive is composed of two separate and distinct water-soluble phenolic resins,- which are to be THE CATALYTIC RESIN The catalytic resin is prepared by reacting a reactive phenol and aqueousform'aldehyde or alcoholic para-formaldehyde in alkaline medium, or initiating the reaction in acid medium and completin it in alkaline medium, at a temperature sufficient to cause reaction but below 70 C., and preferably at a resin solids concentration of about Soto 40 per cent. A reactive phenol is one which'contains no substituents in either the ortho or para position to the hydroxy group. Mixtures of such reactive'phenols, or consisting predominantlyof the same, may also be used. The reaction is'faster when initiated in an acid medium than in an alkaline medium, but when an acid medium is used in this way, caustic alkali is added after phase separation occurs but prior to formation of alkali-insoluble resin and the condensation'is completed under alkaline conditions. The amount of alkali so added is sufficient to produce in the mixture an alkalinity approximately equal to that obtained by carrying out the reaction from the beginning in an alkaline medium of suitable strength.

The mol ratio of formaldehyde to the phenol should be between 2.25 and 3.5 mols CHzO per mol of phenol. The peculiar properties of this resin are not obtained in measurable degree if less than 2.25 incl proportion is used, while more than 3.5 mols is an excess of the reactable proportion. When the reaction is carried out in alkaline medium, alkali metal hydroxide, e. g. sodium hydroxide, is added to the reaction mixture in proportion of 0.5 to 1.0 mol per mol of phenol. The materials, phenol, aqueous formaldehyde and aqueous alkali metal hydroxide, are mixed in desired proportions within the limits just stated, and the mixture is cooked at a temperature below 70 0., preferably about (3., until a suitable viscosity, on the order of 10 to 350 centipoises, or more, is attained, whenmeasured at 25 C. in aqueous solution at 30 per cent solids concentration. If necessary, water may be added during the reaction or to the reaction product to adjust the resin solids content of the same to from 30 to 40 per cent. The time of cooking will vary with the ratio of formaldehyde to phenol, and with the selected phenol. When phenol itself is used the reaction time-with alkali catalyst may vary from 40 to 50 hours or more at a CHzO/phenol ratio of 2.5, while at a ratio of 3.5 the time will be'reduced to about 15 to 20 hours. When the phenol 'used is meta-cresol, under otherwise similar conditions, the reaction time is on the order of 12 to 16 hours at a CHzO/cresol ratio of about 2.5.

The preparation of the nucleated resin with the alkali included in the starting materials, as shown above, requires an extended cooking time at temperatures below 70 C; "The time can be greatly shortened, if the condensation reaction is initiated with a mineral acid catalyst, e. g. hydrochloric acid or sulphuric acid, and then completed with the alkaline catalyst. In this way the resin is advanced in the acid stage at a tempera-' ture below 70 C. to a point short of that. where it becomes alkali-insoluble, and then alkali is added in amount suflicient to neutralize the acid and produce an alkali concentration between'0-.5-

and 1.0 mol perm'ol of phenol originally'pres'ent, after which the" reaction is"cont'inued 't'o completion in the alkaline stage. Bysuchproced'ure the total time required may ber'edu'ced to from 5 to hours, or thereabout. The acid catalyst is added to the initial reaction charge as aqueous solution in amount ontheorder of. about 0.05 to 0.15 mol per mol of phenol. Inlconverting from the acid tothe alkaline stage, the acid may be neutralizedwith ammonia, if desired, in'which case alkali metal] hydroxide' is then added in amount required to,raise the alkalinity of the neutralized mixture .td the desired degree.

The reaction'product' made by either modification of procedure, when examined at highvma nification"(e. g- 2%,000'X) in. an elect'ron microscope, exhibits a, peculiari'tyofjstructure not observed in phenol aldehydej condensation productsmade' outside of 'thestated range of proportions and conditions This structure is characterized by numerous, well defined small dense spherical nuclei, which appeartogbe active, condensation centersff The usual type of "watersoluble 'heat-hardenablef. phenol-formaldehyde resin, made with" an' 1alkaline; catalyst, does not have this characteristic nucleateds'trueture, but in the electron microscopeappea'rs to consist of large irregularly shaped'areasjWithoutweIl defined boundaries. When such nucleated, resin is mixed with a non-nucleated'phenol aldehyde' resin, it apparently activates or catalyses the condensation of the 'latter and causes outing in a shorter time'than if the nucleated resin were not present. Possibly the nuclei act as" a seed around which condensation of 'themass proceeds at an acceleratedrate' Inthe claimsjthe term nucleated means havingfa structure showingnuclei as defined above, and the'term non-nucleated means having" a structure in which the saidnuclei are absent.

Such nucleated resin, ma de as described, is not of itself a good adhesive, since it has too little penetratin power to"form a strong bond with a wood surface. We have found,"however, that the admixture of a low molecular weight water-soluble non-nucleated phenol-formaldehyde resin with the nucleated resin increases the penetrating power and forms an adhesive mixture which hardens or cures rapidly at a moderate temperature, giving a s'trongvbqnd not onlywith dry,jbut also with wet, veneer."

THE BAsnREsIN The base resin to beused with our nucleated catalytic resin is an alkali-catalyzed water-solu- 4 ble non-nucleated heat-hardening phenol-form aldehyde resin with colloidal aggregates of a wide range of molecular weight, which under the electron microscope appear as highly irregular areas of variable density. It is prepared from a mixture of the phenol, aqueous formaldehyde and aqueous alkali metal hydroxide, in which the mol ratio of formaldehyde to phenol is from 1.4 to 3.0, and of alkali metal hydroxide to phenol is between 0.5 and 1.0. The mixture is cooked under reflux at a temperature between 90 C. and the boiling point until a suitable viscosity, e. g. 200 to 500 centipoises, or more, is reached, with a resin solids content on the order of 30 to 40 per cent.

THE ADHESIVE MIXTURE resins'maybevaried according to the conditions. under which they are to be used. For use withdry veneer. (0 to 3.per cent moisture) as little as 10 parts of catalytic resinto 90 partsof. base resin is satisfactory. For. veneers. containing 7 to 10 per cent moisture.preferredproportions ,are 20'to 30 parts of catalyticgresin and." to '70v parts of base resin. Such mixtures aresuitable as well for dry veneers. Larger proportionsof catalytic resin may be used, up to ab o,'ut.8 0 percent, but with little or nor further advantage. There should always-be a substantial proportion of base resin in the. mixture, preferably 20 .per cent or more, in. order todevelop thedesired adhesive properties of the mixture.

The mixing of the two resins can be done by any usual means, in avessel provided with-mechanical stirrer. In making the mix a vfiller, such as wood flour, is usually added to increase body of the mixture to a suitablespreading consistency, and water may be added, if necessary, to adjust the resin solids content of themix to the, desired degree. Atypical formulationfor dry veneers is the following, in parts by weight:

Formulation I Catalytic resin 10 Base .resin Water I 20. Walnut shell flour 15 A typical formulation for wet veneers. (7 .to. 10 percent moisture) is:

These formulations are suggestivemerely, and not limiting. The proportions ofcomponents can be variedto suit particular conditions and-in accordance with the solids content of the resins and the ere cy. es red i 'i i Themixed adhesive is applied and spread in usual manner formakingply'wood assemblies. It

is adaptable to considerable variationof. assembly time, for example, from as low as .5 minutes.

to as much as .1 hour.

The appended examples show various,.formu.-

las for making the mixedadhesives of the inventlon. v o ed. by i s q ne he a hesi properties of the mixtures for making plywood.v

For comparison, examples are given of the re- 5 suits obtained with phenolic adhesives of the prior art. For the purpose of making accurate comparisons, the tests were standardized in detail conforming to practice in the plywood industry.

In the curing test the phenolic resin solution, with 9 per cent of walnut shell flour added to it, is applied at the rate of 6 grams per 8" x 8" area. (equivalent to 30 lbs/1000 sq. ft.) to one side of each of two 8" x 8" x squares of dry Douglas fir veneer, which are then laid with grain direction at right angles and with the glue side bearing on opposite sides of an 8" x 8" x A" square of the same veneer placed between them, forming a dressed 3-ply assembly. Fifteen minutes after the glue is applied the assembly is placed in a steam-heated press set at the temperature of the test, and unless otherwise stated, a pressure of 175 pounds per square inch is applied for 5 minutes, after which the plywood piece is removed and allowed to cool to room A temperature. Each plywood square is cut into 1" x 3 strips which are notched as described on page 5 of Commercial Standard CS45-47, and the shear strength tested (1) on the dry specimen, (2) after hours soaking in cold water and (3) after 4 hours immersion in boiling water. The tests reported are the average of at least 4 strips in each test. The ruptured surface of each test specimen is measured to obtain an estimate of the total area of the break in which the failure was caused by a split in the wood rather than by cleavage of the glue from the Wood, and is reported as per cent wood failure. The values shown in the tabulated results are expressed as two numbers joined by a hyphen (e. g. 278-85), the first number (278) being the pounds per square inch shear strength and the second number (85) being the per cent wood failure. For practical purposes either a shear strength of 200 or more, or a per cent wood failure or 85 or more, is considered to be good.

In the wet veneer gluing test Douglas flr veneer test specimens are used which are conditioned to a moisture content of '7 to 9 per cent. To the phenolic resin solution 15 per cent of walnut shell flour is added. The plywood assembly is laid up with 5 plies 12" x 12", the center ply being and the other four thick, only the three inner plies being glued together, with glue applied at the rate of lbs./ 1000 sq. it. After a certain time the assembly is hot-pressed according to times and temperatures as shown in the tables. The glued panels are stacked hot and allowed to cool slowly for 3 hours, then tested for shear strength a viscosity of 938 centipoises at 90 F. (32 C.).

B. A mixture was made containing:

Phenol (90%) 410.3 gm., 3.93 mols CI-IzO (37%) 716.0 gm., 8.84 mols NaOH (50%) 47.2 gm., 0.59 mol The mixture was heated at refluxing temperature for 70 minutes, when it was partially cooled and the following materials added:

NaOH (50%) 141.4 gm., 1.77 mols NH; (28%) 8.9 gm.

H2O 102.0 gm.

The resulting solution contained 37 per cent of resin solids, the mol ratio of phenol-CI-hO-NaOH being l-2.25-0.6.

C. A mixturewas made containing:

Phenol (90%); 407.7 gm., 3.90 mols CI-IzO (37%) 950.0 gm., 11.70 mols NaOH (50%) 93.6gm., 1.17 mols The mixture was heated at reflux temperature for minutes, cooled and held at 84 C. for 12 minutes, again cooled and held at 68 C. for 17 minutes, and then heated at 80 C. for 10 minutes. At this point further alkali was added, as follows:

NaOI-I 93.6 gm., 1.17 mols NH3 (28%) 99.1 gm.

H2O 12.0 gm.

This gave a resin solution of 37 per cent solids content having a viscosity of 101 centipoises at 30 F. The mol ratio of phenolCH2O-NaOH was l30.6.

D. The following quantities of material were. taken:

Phenol (100%) -1 422.6 gm., 4.50 mols. 01-120 (37%) 730.0 gm., 9.00 mols NaOH (50%) 338.0 gm., 4.22 mols To a mixture of the phenol and formaldehyde was added one-tenth of the sodium hydroxide solution, and the mixture heated at a refluxing temperature while the remainder of the sodium hydroxide solution was added in nine equal portions 10 minutes apart, with 70 grams of dilution water added at the end. The final viscosity was 340 centipoises after a total cooking time of 2 hours and 45 minutes at refluxing temperaiiuge. The mol ratio of phenol-CI-IzO-NaOH was The above four resins were tested according to the curing test previously described, with results as shown in Table I.

The mixture was heated on a steam bath under reflux for 30 minutes, the cooked mixture having 7 as described above under the curing test. Table I EXAMPLE 1 For purpose of comparison four resins were Shear strength and percent; made according to the prior art and tested in R I Press wood more the manner described above. These resins were 0 m H essentially non-nucleated when examined in the Dry waoter electron microscope.

A. A mixture was made consisting oflghlengl g 12M 11M rma e e 20-60 160-17 187-52 (90 per cent), 37 per cent aqueous fo y 130 23%? 239434 194% and 50 per cent aqueous sodium hydroxide in the 133-30 117-70 258- 23am following proportions. 130 253438 225% 203% a are are ..r 2 P Material Amount Mols M01 ratio 130 347%,) fig 12 5 153-42 168-40 193-82 Phenol 05 E 205-98 242-94 272-96 011,0 37%). 6.15 NaOH (50%)... 1. 54 0.75 Resins B and C were subjected to the wet veneer gluing test as described, with assembly times varying from 10 to 45 minutes, and pressed for 6 7 minutesat 140 C. All samples were-completely delaminated. Resin D was also subjected to the wet veneer testat'132 C., the samples likewise being delaminated.

EXAMPLE 2 A catalytic resin was preparedfrom the following materials:

Material Amount Mols M01 ratio Gm.- Phenol (90%) 320.6 3.08 1 CHzO (37%).... 623. 7.69 2. NaOH (50%) 173.0 2.16 .7

The materials were mixed and the mixture cooked at 60 C. until its viscosity was 197 centipoises, when 340 cc. of water was added to bring the'resin solids content to percent.

A base resin was prepared from the following materials:

Material Amount Mols M01 ratio Gm. P118110! (90%) 399. 3 3. 82 1 These materials werem'ixedan'd cooked under refiux at 90 to 95 C. until the viscosity of the mixture was 220 centipoises.

A mixture was made consisting of 20 per cent of the catalytic resin and 80 per cent of the base resin, which was used to make up plywood panels from both dry and wet veneers for test accord-' ing to the procedures described. The results of the curing test on panels made from dry veneers are shown in Table II(a), and of the gluing test- Acatalytic resin was prepared from the' following materials:

Material Amount Mols gig The materials were'mi'xed and cooked at 60 C. until a viscosity of 200 centipoises was reached. 20 parts of this resin was mixed with parts of the base resin of Example 2, to form a composite adhesive. Plywood panels were prepared from veneers of 8 per cent moisture'content and subjected to the gluing test'as described, with results as shown in Table III.

Table III Shear strength and percent Press Assembly 4 wood failure time,

Time, Temp., Cold Boiling min. C. y water Water EXAMPLE 4 A catalytic resin was prepared with meta-cresol as the phenol constituent. The materials were mixed in the following proportions:

- M01 Material Amount Mols ratio Gm. m-Cresol 305. 4 2. 83 1 The mixture was heated at 60 C. until the viscosity was centipoises. 20 parts of this resin was mixed with 80 parts of the base resin of Example '2, and the mixed adhesive was tested in the same manner described in the preceding examples, with results as shown in Tables IV(a) and IV(b) Table IV(a).-Curing test Shear strength and percent Press wood failure temo, Cold Boiling D ry water water Table IV(b) .-Wet veneer test Shear strength and percent Assembly P1055 wood failure time, min

' Time Temp; Cold Boiling min. 0. Dry water water EXAMPLE '5 A catalytic resin was prepared from a mixture of phenol and meta-cresol, the materials being mixed in the following proportions:

Mol Material Amount Mols ratio Gin.

9 This mixture was cooked at 60 C. until the viscosity was 125 centipoises. 20 parts of the resin was mixed with 80 parts of the base resin of Example 2, and plywood test specimens were prepared in the manner already described and tested according to the wet veneer gluing test, with results as shown in Table V.

A base resin was prepared from a mixture of the following materials:

. Mel Material Amount Mols ratio Gm. Phenol (90 214. 2 2.05 1.0 CHzO (37%).... 333.0 4.10 2. NaOH (50%)... 154.0 1.93 .94 B20... 166.0

The mixture was refluxed at boiling temperature until its viscosity was 246 centipoises. Plywood test specimens were, prepared as previously described from (1) the base resin alone, (2) parts of the catalytic resin of Example 2 and 90 parts of the base resin, and (3) 30 parts of the same catalytic resin and 70 parts of the base resin. These samples were subjected to the curing test at temperatures of 110, 120 and 130 C., with results as shown in Table VI.

The results show that the base resin (No. 1) did not cure completely until heated at 130 C. under the test conditions, whereas the composite resins of the invention (Nos. 2 and 3) cured at 110 C.

EXAMPLE 7 To show the superiority of the composite adhesive of the invention as compared with the catalytic resin alone under the wet veneer gluing test, plywood specimens were prepared from (1) the catalytic resin of Example 3 alone and (2) a mixture of 20 parts of this catalytic resin and 80 parts of the base resin of Example 2, and submitted to the test, with results as shown in Table VII.

Table VII Shear strength and peweut Asscm- Press wood failure 1 Resin ggg min. Time, Temp., Dr Cold Boiling min. C. y water water EXAIVIPLE 8 A catalytic resin was prepared by procedure in which the condensation was initiated in acid medium and completed in alkaline medium. The initial charge consisted of the following:

Mol Matenal Amount Mols ratio Gm. Phenol (100% 306 3. 2s 1 01120 (37% 792 9.78 3 H01 (12N) 6. 13 .168 .05

The materials were mixed and heated at 60 C. with stirring for 7 hours. Then 392 cc. of water and 196.8 gm. of .50 per cent NaOI-l solution were added, to give a resin solids content of 30 per cent, and an excess of 0.7 mol NaOH per mol of phenol after neutralization of the acid. The addition of water and NaOH solution reduced the previously viscous mixture to a viscosity of 30 centipoises. Heating was continued at 60 C. for 5 hours until the viscosity was 100 centipoises.

This resin was mixed with the base resin 01? Example 2 in proportion of 20 parts of the former to parts of the latter, and the mixture was used to prepare plywood panels which were submitted to the wet veneer gluing test, with results as shown in Table VIII.

This test was run to study the effect of varying the ratio of formaldehyde to phenol in the base resin upon the properties of the mixed resin obtained by mixing with a particular catalytic resin. A catalytic resin was prepared from the following materials:

. M01 Matenal Amount Mols ratio Gm. Phenol 1142 12.17 1 omo 37%) 2960 36.5 3 NaOH (50%) 686 8. 5s .7

The materials were mixed and heated at 60 C.

for 22 hours until a viscosity of centipoises was reached. A series of base resins was prepared from the same materials, in which the mol ratio of formaldehyde to phenol was 1.4, 1.7, 2.0, 2.5 and 3.0, respectively, and the mol ratio of NaOH to phenol in each case was 0.94. The mixtures were cooked at reflux temperature until the viscosity increased to about 400 centipoises. Mixtures were made containing 20 parts of the catalytic resin and 80 parts of the respective base resin, plywood panels were prepared from dry and from wet veneers, respectively, by pressing at 200 pounds/square inch, and subjected to the curing test and the wet veneer gluing test, with results as shown in Tables IX(a) and IX-(b). respectively.

Table lXla) ..,Cur.ing test Shear strength and percent GHzO/Phenol Press {31mm ratio qinbase temr,

Cold Boiling Dry water Water Table IX(b).-.-Wet veneer test [Assembly time-l0 minutes] Shear strength and percent C1120 [Phen 01 Press 7 Wood failure ratio of base 5111 Time, Temp, Dr Cold Boiling min. 0. y water water The values obtained in the .curing test on plywood made from dry veneer do not vary greatly, and the same is true in the gluing test on plywood made from wet veneers, except in the case of the panels made with adhesive containing the base resin having a 1.4 CHzO/phenol ratio, where the values are definitely lower.

The effect of varying the proportions of a catalytic resin and a. base resin upon the adhesive properties of the mixed resin is shown in this test. A base resin was prepared from the follow -ma er al M01 Material Amount Mols ratio Gm. Phenol (100%) 1,092 11.63 1 GHzO (37% 1, 603 19. 8 1. 7

12 .T bl

Cold water Boiling water 1 Panel blistered. 9 Delaminated.

With 100 parts of :base resin in the adhesive the panel blistered and the portions that did stick had low per cent wood failure. The panel put together with a mixture containing 5 per cent of the catalytic resin also blistered and the portions which did stick in testing showed low wood failures, and the test strips also delaminated in boiling Water. In both cases the poor bond resulted probably on account of insufficient cure together with an excessive migration of resin from the glue line, caused by the thinning effect of the veneer moisture. All mixtures containing from to 20 parts of the base resin, and from 10 to 80 parts of the catalytic resin produced panels having a high per cent of wood failure and from fair to high shear strength. The panels made with parts of the catalytic resin, on the other hand, showed a low value for per cent wood failure, due to poor penetration.

It is sometimes advantageous to include a small amount of starch or a native protein, 1. e. one of vegetable .or animal origin, in the mixture of materials used for preparing the catalytic resin. Example of .such protein are casein and soyabean alpha protein. Such additive does not materially change the adhesive properties of the resins made by mixing the catalytic resin with a base resin, but it improves the water dispersability of the resin. A typical formula for making such a resin is:

Material Mols Mol ratio The mixture is cooked at a temperature below 70 C. to a suitable viscosity in the manner previously described. When mixed in suitable proportion with a base resin an adhesive is obtained having equivalent properties to those shown in the examples herein, for application to dry or wet veneers.

We claim:

1. A water-soluble phenolic resinous composition, characterized by having a nucleated structure and adapted to be mixed with a non-nucleated alkaline phenolic resinous composition to produce an adhesive capable of forming on curing a strongly bonded plywood from wet veneers, which consists essentially of alkali metal hydroxide and the condensation product of a reactive phenol containing no substituents in positions ortho or para to the hydroxyl group with from 2.25 to 3,5 molar proportions of formaldehyde, the alkali metal hydroxide being in proportion of from 0.5 to 1.0 mol per mol of the phenol, such condensation product being formed by heating the reactants in the presence of water and a condensation catalyst at a temperature below 70 C. sufiicient to cause condensation of the phenol and formaldehyde, the reaction being at least completed in the presence of the specified amount of alkali metal hydroxide to a viscosity of from to about 350 centipoises measured at C. and a resin solids content of per cent.

2. A water-soluble phenolic resinous composition, characterized by having a nucleated structure and adapted to be mixed with a nonnucleated alkaline phenolic resinous composition to produce an adhesive capable of forming on curing a strongly bonded plywood from wet veneers, which consists essentially of sodium hydroxide and the condensation product of a reactive phenol containing no substituents in positions ortho or para to the hydroxy group with from 2.25 to 3.5 molar proportions of formaldehyde, the sodium hydroxide being in proportion of from 0.5 to 1.0 mol per mol of the phenol, such condensation product being formed by heating the reactants in the presence of water and a condensation catalyst at a temperature below 70 C. suflicient to cause condensation of the phenol and formaldehyde, the reaction being at least completed in the presence of the specified amount of sodium hydroxide to a viscosity of from 10 to about 350 centipoises measured at 25 C. and a resin solids content of 30 per cent.

3. A water-soluble phenolic resinous composition, characterized by having a nucleated structure and. adapted to be mixed with a non-uncleated alkaline phenolic resinous composition to produce an adhesive capable of forming on curing a strongly bonded plywood from wet veneers, which consists essentially of the reaction product formed by heating a reactive phenol containing no substituents in positions ortho or para to the hydroxyl group with from 2.25 to 3.5 molar proportions of formaldehyde in aqueous mixture in the presence of from 0.5 to 1.0 molar proportion of sodium hydroxide at a temperature below 70 C. sufiicient to cause condensation of the phenol and formaldehyde to a viscosity of from 10 to about 350 centipoises measured at 25 C. and a resin solids content of 30 per cent.

4. The method of making a nucleated watersoluble phenolic resin, which comprises forming an aqueous mixture of a reactive phenol containing no substituents in positions ortho or para to the hydroxyl group with from 2.25 to 3.5 molar proportions of formaldehyde and from 0.5 to 1.0 molar proportion of alkali metal hydroxide and heating the mixture at a reaction temperature below 70 C. sufiicient to cause condensation of the phenol and formaldehyde, to a viscosity of from 10 to about 350 centipoises measured at a temperature of 25 C. and a resin solids content of 30 per cent.

5. Method according to claim 4, in which the alkali metal hydroxide is sodium hydroxide.

6. Method according to claim 4., in which the reaction temperature is approximately 60 C.

7. The method of making a nucleated watersoluble phenolic resin, which comprises forming an aqueous mixture of a reactive phenol containing no substituents in positions ortho or para to the hydroxyl group with from 2.25 to 3.5 molar proportions of formaldehyde, acidifying with mineral acid, heating the mixture at a reaction temperature below 70 C. until partial condensation occurs but not so long that alkali-insoluble resin is formed, adding alkali metal hydroxide in amount suiiicient to neutralize the acid and form an excess of alkali of from 0.5 to 1.0 molar proportion relative to the phenol originally employed, and continuing the reaction at a temperature below 70 C. to a viscosity of from 10 to about 350 centipoises measured at a temperature of 25 C. and a resin solids content of 30 per cent.

8. Method according to claim 7, in which the mineral acid is hydrochloric acid.

9. Method according to claim 7, in which the alkali metal hydroxide is sodium hydroxide.

10. Method according to claim 7, in which the reaction is carried. out at a temperature of approximately 60 C.

11. A water-soluble phenolic resin adhesive consisting essentially of 100 parts of a mixture of (a) from 20 to 90 parts of an essentially non-nucleated base resin, which is the condensation product prepared by heating an aqueous mixture of a reactive phenol containing no substituents in positions ortho or para to the hydroxyl group with from 1.4 to 3.0 mols of form.- aldehyde and from 0.5 to 1.0 mol of alkali metal hydroxide per mol of the phenol at a temperature between 90 C. and the boiling point of the reaction mixture to a viscosity of from 200 to 500 centipoises measured at 25 C. and a resin solids content of 30 per cent, and (b) from to 10 parts of a nucleated catalytic resin, which is the condensation product prepared by heating an aqueous mixture of such reactive phenol with from 2.25 to 3.5 mols of formaldehyde per mol of the phenol and a condensation catalyst at a temperature below 70 C. sufiicient to cause condensation of the phenol and formaldehyde, the reaction being at least completed in the presence of from 0.5 to 1.0 mol of alkali metal hydroxide per mol of the phenol to a viscosity of from 10 to about 350 centipoises measured at 25 C. and a resin solids content of 30 per cent.

12. A water-soluble phenolic resin adhesive consisting essentially of 100 parts of a mixture of (a) from 20 to parts of an essentially non-nucleated base resin, which is the condensation product prepared by heating an aqueous mixture of a reactive phenol containing no substituents in positions ortho or para to the hydroxyl group with from 1.4 to 3.0 mols of form aldehyde and from 0.5 to 1.0 mol of alkali metal hydroxide per mol of the phenol at a temperature between 90 C. and the boiling point of the reaction mixture to a viscosity of from 200 to 500 centipoises measured at 25 C. and a resin solids content of 30 per cent, and (b) from 80 to 10 parts of a nucleated catalytic resin, which is the condensation product prepared by heating an aqueous mixture of such reactive phenol with from 2.25 to 3.5 mols of formaldehyde per mol of the phenol and from 0.5 to 1.0 mol of alkali metal hydroxide per mol of the phenol at a temperature below 70 C. sufiicient to cause condensation of the phenol and formaldehyde until the viscosity of the mixture is from 10 to about 350 centipoises measured at 25 C. and a resin solids content of 30 per cent.

13. A water-soluble phenolic resin adhesive consisting essentially of parts of a mixture of (a) from 20 to 90 parts of an essentially nonnucleated base resin, which is the condensation product prepared by heating an aqueous mix- .ture of phenol with from 1.4 to 3.0 molsof formaldehyde and from 0.5 to .1.0 mo1 of sodium hydroxide per mol of phenol at a temperature between 90 C. and the boiling point of the reaction mixture to a viscosity of from 200' to 500 centipoises measured at 25 C. and a, resin solids content of 30 per cent, and (-b) from 80 to 10 parts of a nucleated catalytic resin, which is the condensation product prepared 'by heating an aqueous mixture of phenol with from 2.25 to 3.5 mols of formaldehyde .per mol of phenol and a condensation catalyst at a temperature of approximately 60 C., the reaction being at least completed in the presence of from 0.5 to 1.0 mol of sodium hydroxide per-mol of the phenol to a viscosity of from 10 to about :350 centipoises measured at 25 C. and a resin solids content of 30 per cent.

14. A water-soluble phenolic resin adhesive consisting essentially of 100 parts of a mixture of .(a) from to 90 parts of an essentially nonnucleated base resin, which is the condensation product prepared by heating an aqueous mixture of phenol with from 1.4 to 3.0 mols of formaldehyde and from 0.5 to 1.0 mol of sodium hydroxide per mol of phenol at a temperature between 90 C. and the boiling point of the reaction vmixture to a viscosity of from 200 to 500 centipoises measured at C. and a resin solids content of per cent, and (b) from 80 to 10 parts of a nucleated catalyticresin, which is the condensation product prepared by :heating 'an aqueous mixture of phenol with from 2.25 to 3.5 mols of formaldehyde per 'mol of phenol and from 0.5 to .laO mol of sodium hydroxide at a temperature of approximately C. until the viscosity of the mixture is from 10 to about 350 centipoises measured at 25 C. and a resin solids content of 30 percent.

.15. Plywood bonded with the adhesive defined in claim 11.

16. Plywood bonded with the adhesive defined .in claim 12.

17. Plywood bonded with the adhesive defined in claim 13.

18. Plywood bonded with the adhesive defined in claim 14.

PAUL G. SCHRADER. ALEX. M. PARTANSKY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,091,183 Murray et al. Aug. 24, 1937 2,351,716 Smith June 20, 1944 2,360,376 Van Epps Oct. 17, 1944 2,485,527 Cardwell Oct. 18, 1949 

11. A WATER-SOLUBLE PHENOLIC RESIN ADHESIVE CONSISTING ESSENTIALLY OF 100 PARTS OF A MIXTURE OF (A) FROM 20 TO 90 PARTS OF AN ESSENTIALLY NON-NUCLEATED BASE RESIN, WHICH IS THE CONDENSATION PRODUCT PREPARERD BY HEATING AN AQUEOUS MIXTURE OF A REACTIVE PHENOL CONTAINING NO SUBSTITUENTS IN POSITIONS ORTHO OR PARA TO THE HYDROXYL GROUP WITH FROM 1.4 TO 3.0 MOLS OF FORMALDEHYDE AND FROM 0.5 TO 1.0 MOL OF ALKALI METAL HYDROXIDE PER MOL OF THE PHENOL AT A TEMPERATURLE BETWEEN 90* C. AND BOILING POINT OF THE REACTION MIXTURE TO A VISCOSITY OF FROM 200 TO 500 CENTIPOISES MEASURED AT 25* C. AND A RESIN SOLIDS CONTENT OF 30 PER CENT, AND (B) FROM 80 TO 10 PARTS OF A NUCLEATED CATALYTIC RESIN, WHICH IS THE CONDENSATION PRODUCT PREPARED BY HEATING AN AQUEOUS MIXTURE OF SUCH REACTIVE PHENOL WITH FROM 2.25 TO 3.5 MOLS OF FORMALDEHYDE PER MOL OF THE PHENOL AND A CONDENSATION CATALYST AT A TEMPERATURE BELOW 70* C. SUFFICIENT TO CAUSE CONDENSATION OF THE PHENOL AND FORMALDEHYDE, THE REACTION BEING AT LEAST COMPLETED IN THE PRESENCE OF FROM 0.5 TO 1.0 MOL OF ALKALI METAL HYDROXIDE PER MOL OF THE PHENOL TO A VISCOSITY OF FROM 10 TO ABOUT 350 CENTIPOISES MEASURED AT 25* C. AND A RESIN SOLIDS CONTENT OF 30 PER CENT. PLYWOOD BONDED WITH THE ADHESIVE DEFINED IN CLAIM
 11. 